User Manual of EM730/EM730E Series Inverter
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return (crcH<<8) | (crcL);
}
11.3.7
Exception response
When the master station sends a request to the slave station, the master station expects a
normal response. Query of the master station may result in one of the following four events:
If a request without communication error is received from the slave station and can be
processed properly, a normal response will be returned by the slave station.
If the slave station does not receive a request due to communication errors, no
message will be returned. This will be regarded as a timeout by the slave station.
If the slave station receives a request but detects a communication error (parity,
address, frame error, etc.), no response will be returned. This will be regarded as a
timeout by the slave station.
If the slave station receives a request without communication error but cannot process
the request (e.g. a request to read the non-existent register), the slave station will
return an exception response and the master station will be informed of the actual
error.
The exception response message has two fields different from those of the normal
response:
Function code field: In the normal response, the slave station copies the function code
of the original request in the corresponding function code field. The MSB values of
all function codes are 0. In the exception response, the MSB of the function code is
set to 1 by the slave station. That is,
the exception response function code =
normal response function code + 0x80
.
Data field: The slave station can return the data from the data field in the normal
response and exception code in the exception response. For the defined exception
codes, Table 4-33 Definitions of Exception CodesTable 4-33.
Table 4-33 Definitions of Exception Codes
Exception
code
Item
Meaning
01H
Illegal function
The function code received by the slave station (inverter) is
beyond the configured range (see 11.3.3Function
02H
Illegal data
The data address received by the slave station (inverter) is not
